1. Field of the Invention
This invention relates to a water-impermeable rubber composition which is highly adhesive to a refrigerant gas-impermeable resin even at a high temperature without the aid of any adhesive layer. It also relates to a rubber-resin laminate formed by adhesion using such a rubber composition, and having high impermeability to both water and a refrigerant gas. It further relates to a fluid-impermeable hose having an inner wall layer formed of such a laminate.
2. Description of the Related Art
A hose used for transporting a refrigerant in an air-conditioning system for an automobile or a room, or the like usually has a wall having an inner layer. an outer layer and a reinforcing layer disposed therebetween. There has recently been made a change in the refrigerant to be used in an air-conditioning system from, for example, what is known as R-12 to R-134, with a resultant change in the rerigerator oil to be used. These changes have brought about a demand for a refrigerant hose having a double inner wall layer formed of an inner layer of a resin which is impermeable to a refrigerant gas, and an outer layer of rubber which is impermeable to water. If those two layers are poorly adhesive to each other, the refrigerant gas is likely to collect therebetween, resulting in the separation of the layers as a defect of a fluid-impermeable hose. Therefore, an adhesive is used to bond the two layers more tightly together. The use of an adhesive, however, gives rise to a number of problems including environmental contamination by the solvent of the adhesive.
Thus, there have been proposed various hoses having a rubber layer and a resin layer adhered without the aid of an adhesive layer, through mixing an adhesive material in the rubber composition during the process of vulcanization. For example, Japanese Patent Application Laid Open No. 117178/1995 discloses a composite flexible hose having in its wall an intermediate layer of rubber formed of a composition containing a mixture of butyl rubber and halogenated butyl rubber, a brominated alkylphenol-formaldehyde resin (Br-APF) as a resinous vulcanizing agent and silicic acid or a salt thereof as an adhesive material. The adhesive material makes the rubber layer adhesive to the innermost layer of a modified polyamide resin. Japanese Patent Application Laid-Open No. 16138/1998 discloses a gas-impermeable reinforced hose having an inner wall layer formed of an inner layer of a modified polyamide resin, an intermediate layer of halogenated butyl rubber and an outer layer of an ethylene-xcex1-olefin-unconjugated diene copolymer. The halogenated butyl rubber contains Br-APF and a modified liquid polyisoprene as an adhesive material.
When any such hose is used in, for example, an air-conditioning system for an automobile, it is exposed to a high temperature, since it is usually installed in its engine compartment. The high adhesion between its rubber and resin wall layers, required in an environment having a normal temperature, is all the more necessary in environments having an elevated temperature. Those layers, however, usually have smooth curved surfaces which are not easy to keep adhering to each other, particularly at a high temperature. The inventors of this invention have found from research work that the adhesion between the polyamide resin layer and rubber layer of the hoses as disclosed in the two Japanese patent applications cited above is satisfactory in an environment at a normal temperature, but not at an elevated temperature.
It is, therefore, an object of this invention to provide a rubber composition which can form a water-impermeable rubber layer adhering satisfactorily even at a high temperature to a refrigerant gas-impermeable resin layer without relying upon any particular adhesive layer.
It is another object of this invention to provide a rubber composition which can form a layer having a smooth curved surface and adhering satisfactorily even at a high temperature to a resin layer having a smooth curved surface without relying upon any particular adhesive layer through an adhesive material mixing procedure.
It is still another object of this invention to provide an advantageous laminate of rubber and resin layers remaining firmly adherent to each other even at a high temperature without having any adhesive layer formed therebetween, through an adhesive material mixing step.
It is a further object of this invention to provide a hose having an impermeable wall formed by a laminate of rubber and resin layers remaining firmly adherent to each other even at a high temperature without having any adhesive layer formed therebetween.
According to a first aspect of this invention, there is, thus, provided a rubber composition comprising as a base material at least one rubber selected from the group consisting of butyl rubber (IIR) and halogenated butyl rubber (halogenated IIR), 0.5 to 5 parts by weight of at least one resorcinol compound as an adhesive material per 100 parts by weight of the base material and 3 to 15 parts by weight of at least one vulcanizing agent selected from the group of consisting of an alkylphenol-formaldehyde resin (APF) and a brominated alkylphenol-formaldehyde resin (Br-APF) per 100 parts by weight of the base material, wherein the composition contains at least 0.5% by weight of bromine.
The rubber composition according to the first aspect of this invention can form a rubber layer remaining firmly adherent to a polyamide or polyester resin layer even at a high temperature. A refrigerant hose, as in an air-conditioning system, requires a high adhesion between its rubber and resin wall layers at a high temperature. If their adhesion is not satisfactory, their separation is likely to occur upon creation of a negative pressure in the hose at a high temperature. In this connection, the rubber composition according to this aspect is very useful. The adhesion at a high temperature in the context of this specification differs from an adhesive strength after hot air aging as discussed in Japanese Patent Application Laid-Open No. 117178/1995.
A rubber composition containing a smaller amount of adhesive material or of bromine than that stated above fails to form a satisfactorily adhesive layer at a high temperature. A composition containing a smaller amount of vulcanizing agent than stated above fails to form a vulcanized product having satisfactory physical properties. A composition containing a larger amount of adhesive material or vulcanizing agent than the range stated above is less easy to extrude and work with because of too rapid scorching.
The composition according to this aspect does not require any particular adhesive to ensure its adhesion to a resin layer, since the adhesive material which has been mixed in ensures its firm adhesion even at a high temperature. The adhesive material also ensures a firm adhesion of a layer of the composition to a reinforcing layer formed around it of yarns treated with RFL (resorcinol/formalin/latex), since it is highly reactive with RFL.
According to a second aspect of this invention, the halogenated butyl rubber is preferably brominated butyl rubber (Br-IIR). The composition containing brominated butyl rubber forms a layer showing a particularly firm adhesion to a polyamide or polyester resin layer at a high temperature. Although no definite reason is known as yet, it is considered that the bromine which the rubber contains may have some effect or other on the vulcanization of the resin. Moreover, the use of rubber containing bromine makes it easier to produce a composition containing at least 0.5% by weight of bromine, thus providing a greater range of freedom in selecting APF or Br-APF, or a mixture thereof as the vulcanizing agent.
According to a third aspect of this invention, the resorcinol compound is resorcinol, or another compound containing a resorcinol structure at each end of its molecule. The composition containing any such compound forms a layer showing a particularly firm adhesion to a polyamide or polyester resin layer at a high temperature.
According to a fourth aspect of this invention, the composition further comprises not more than 5 parts by weight of at least one of methylol melamine and hexamethylene tetramine per 100 parts by weight of the base material. It forms a layer showing a still improved adhesion to a polyamide or polyester resin layer. A composition containing a larger amount of methylol melamine or hexamethylene tetramine than the limit given above is likely to have a greater compression set upon vulcanization and a hose formed of this composition is likely to fail to make a tightly sealed joint with another pipe.
According to a fifth aspect of this invention, there is provided a laminate comprising a rubber layer formed of any composition according to this invention as set forth above, and a polyamide or polyester resin layer bonded to the rubber layer by vulcanization. The rubber layer maintains a high adhesion to the resin layer, as stated above.
According to a sixth aspect of this invention, the resin layer is preferably of a polyamide resin, or a resin mixture consisting of 50 to 100% by volume of a polyamide resin and 0 to 50% by volume of a modified polyolefin resin. The polyamide resin may contain xcex5-caprolactam. The modified polyolefin resin is a polyolefin resin modified by its graft polymerization with an unsaturated carboxylic acid or a monomer derived therefrom. The rubber layer maintains a particularly firm adhesion to the resin layer consisting or, or containing a polyamide resin.
According to a seventh aspect of this invention, there is provided a fluid-impermeable hose having a wall formed of an inner layer, an outer layer and a reinforcing layer disposed therebetween, its inner layer being a laminate of rubber and resin layers according to the fifth or sixth aspect of this invention as set forth above. The hose can be installed in, for example, the engine compartment of an automobile as a refrigerant hose in its air-conditioning system without causing any problem, as the two layers forming the laminate remain firmly adhered to each other even at a high temperature and do not allow any refrigerant gas to collect therebetween and cause their separation from each other.
The above and other features and advantages of this invention will become more apparent from the following description and the accompanying drawing.